This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for DEVICE AND METHOD FOR STABILIZING HORIZONTAL TRANSISTOR OF VIDEO DISPLAY APPARATUS earlier filed in the Korean Industrial Property Office on Jun. 21, 1996, and there duly assigned Ser. No. 22948/1996.
1. Technical Field
The present invention relates to a video display device such as a multi-mode monitor for a computer system, and more particularly, relates to a device and process of stabilizing a horizontal transistor of the video display device in which the horizontal transistor can be stably operated with no damage when an operation mode of a video card in the computer system is changed for a visual display of a desired image on a screen.
2. Related Art
Generally, a display device such as a CRT type of monitor is a peripheral device which processes information data received from an information data system such as a computer system and provides a visual display of processed information data on a screen. Such a monitor is typically available in either black and white known as monochrome monitor or high resolution color known as color graphics adapter (CGA), video graphics adapter (VGA) and extended graphics adapter (XGA) monitor. Monochrome, CGA, EGA monitors provide a visual display of graphics data by processing digital signals. VGA monitors, by contrast, provide a visual display of graphics data by processing analog signals. In all display devices, the video signal is typically received from a video card installed in an information data system in accordance with vertical and horizontal synchronous signals for a visual display. Vertical and horizontal synchronous signals exhibit different frequencies according to different operation modes of the video card. For example, in a CGA mode, the vertical and horizontal synchronous signals exhibit frequencies of 60 Hz and 15.75 KHz, respectively. In a VGA mode, the vertical and horizontal synchronous signals exhibit frequencies of 60 Hz and 31.47 KHz, respectively. Similarly, in a XGA mode, the vertical and horizontal synchronous signals exhibit frequencies of 60 Hz and 48.36 KHz, respectively.
Various operation modes may be present in addition to the above operation modes. Likewise, the vertical and horizontal synchronous signals have different frequencies according to the various operation modes. When the operation mode of the video card in the computer system is changed to display a desired signal on the screen of the video display device, the video display device discriminates the changed operation mode on the basis of the frequencies of the vertical and horizontal synchronous signals from the video card and performs an operation in the discriminated operation mode.
A conventional display device generally includes a micro-processor which receives the vertical and horizontal synchronous signals from the video card to control the visual display of information data on a screen, and vertical and horizontal deflection circuits which respectively receive the vertical and horizontal synchronous signals to perform vertical and horizontal deflection, such that an electron beam generated from an electron gun of a CRT is deflected in a regular sequence from an upper left portion to a lower right portion of the CRT by way of a deflection yoke in order to form an image. Using high voltage technology, a high voltage generating circuit such as disclosed, for example, in U.S. Pat. No. 5,438,245 for High Voltage Generating Circuit issued to Kii et al., is included to stably supply a high voltage to an anode of the CRT for forming an image in response to a flyback pulse generated from the horizontal deflection circuit. A video amplifier then serves to amplify video signals R, G and B transmitted from the video card to approximately 40Vpp-60Vpp for providing energy to each picture.
In such a display device, deflection circuits perform either an electrostatic deflection using an electric field or an electromagnetic deflection using a magnetic field. As a result, an image is formed on the CRT type of monitor from the electron beam projected onto a fluorescent surface thereof and by flowing a toothed waveform of electric current into horizontal and vertical coils using the electromagnetic deflection. An example of such horizontal deflection circuit is disclosed in U.S. Pat. No. 4,263,615 for Horizontal Drive Circuit For Video Display issued to Steinmetz et al. Generally, the horizontal deflection circuit includes a horizontal drive circuit and a horizontal deflection output circuit, for generating an output horizontal deflection signal to a deflection yoke connector of the CRT monitor. The horizontal deflection output circuit typically includes a transformer for amplifying a horizontal drive signal and a horizontal transistor which operates in response to an output of the transformer to generate an output horizontal deflection signal.
When the operation mode of the video card is changed, however, the horizontal transistor becomes unstable during a transient state. As a result, the deflection yoke connector of the CRT monitor produces an unstable horizontal deflection magnetic field, and thereby causing an image displayed on a screen to be blurry and unstable. Moreover, a voltage level of a horizontal drive signal generated during a transient time may exceed a rated voltage level of the horizontal transistor which often can damage operation of the horizontal transistor.
Accordingly, it is therefore an object of the present invention to provide an improved video display device.
It is also an object to provide a video display device capable of stabilizing a horizontal transistor incorporated therein for stable operation.
It is another object to provide a process of stabilizing operation of a horizontal transistor in a video display device during a transient period when there is a change in operation mode of a video card installed in a computer system.
These and other objects of the present invention can be achieved by a stabilizing circuit for stabilizing a horizontal transistor of a video display device including a micro-computer for separating vertical and horizontal synchronous signals received from a video card in a computer system and discriminating an operation mode of the video card in response to frequencies of the separated vertical and horizontal synchronous signals so as to control entire operation of the video display device in a discriminated operation mode, a vertical drive circuit including a first phase locked loop circuit for performing a phase locked operation in response to the vertical synchronous signal to produce a vertical drive signal, a horizontal drive circuit including a second phase locked loop circuit for performing a phase locked operation in response to the horizontal synchronous signal to produce a horizontal drive signal, a vertical output circuit for generating a vertical deflection signal in response to the vertical drive signal from the first phase locked loop circuit and applying the vertical deflection signal to a deflection coil, and a horizontal output circuit for generating a horizontal deflection signal in response to the horizontal drive signal from the second phase locked loop circuit and applying the horizontal deflection signal to the deflection coil. The stabilizing circuit includes a transient state detection unit for detecting a transient state of the second phase locked loop circuit due to a change in the operation mode of the video card, and uses the micro-computer to generate vertical and horizontal synchronous signals with frequencies before the change in the operation mode of the video card when the transient state detection unit detects the transient state of the second phase locked loop circuit.
In accordance with another aspect of the present invention, a process of stabilizing a horizontal transistor of a video display device comprises: detecting vertical and horizontal synchronous signals from a video card installed in a computer system and discriminating whether detected vertical and horizontal synchronous signals exhibit frequencies corresponding to an operation mode of the video display device; generating control signals corresponding to the operation mode of the video display device to control the entire operation of the video display device in the corresponding mode, when the detected vertical and horizontal synchronous signals exhibit frequencies corresponding to the operation mode of the video display device; and generating vertical and horizontal synchronous signals with frequencies before a change in an operation mode of the video card when an interrupt signal is generated in response to the mode change.
The present invention is more specifically described in the following paragraphs by reference to the drawings attached only by way of example.